In the conventional electrophotographic image forming apparatuses, an electrostatic latent image formed on a photoconductor is formed into an apparent image with a toner. For example, an electrostatic latent image is formed on a photoconductor, and the electrostatic latent image is developed with a toner to form a toner image. The toner image is usually transferred onto a transfer paper, and fixed onto the transfer paper.
In fixing the toner image onto the transfer paper, a thermal fixing method such as a heating roller fixing method and a heat belt fixing method is generally used for its energy efficiency.
The recent market increasingly has demanded an image forming apparatus with a higher speed and lower power consumption, leading to a demand for a toner having excellent low-temperature fixing properties. To achieve the low-temperature fixing properties of the toner, the softening temperature of a binder resin contained in the toner needs to be lowered. Meanwhile, a low softening temperature of the binder resin degrades the heat-resistant storage properties of the toner, causing the so-called blocking that is a phenomenon such that toner particles fuse with each other particularly under a high temperature environment.
As a technique for solving this problem, use of a crystalline resin as the binder resin for the toner is known. For example, the crystalline resin can rapidly soften at the melting point. As a result, the softening temperature of the toner can be lowered nearly to the melting point of the crystalline resin while heat-resistant storage properties at the melting point or less are kept. Thus, low-temperature fixing properties and heat-resistant storage properties can be met at the same time.
PTL 1 discloses a resin particle containing a crystalline resin. At this time, the resin particle is produced using an aqueous medium, the largest peak temperature (Ta) of heat of fusion is 40° C. to 100° C., the ratio of the softening point to Ta (softening point/Ta) is 0.8 to 1.55, and the conditions:G′(Ta+20)=1×102 to 5×105 [Pa], and  [1]G″(Ta+20)=1×102 to 5×105 [Pa]  [2][G′: storage elastic modulus, and G″: loss elastic modulus] are met.
For example, PTL 1 describes a toner as one example of application of the resin particle.
Unfortunately, if such a crystalline resin is used, a pigment is difficult to introduce into the crystalline resin, reducing the saturation of an image.